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-   -   primus heating system (https://www.wanderlodgeownersgroup.com/forums/showthread.php?t=1857)

aclark 11-01-2008 04:41 PM

primus heating system
Can anybody tell where the power for the circulation pump on the primus heating system come s from? I have no power at the circulation pump.

RGloverii 11-01-2008 09:05 PM

There is a relay mounted to your firewall which powers each Primus pump. It powers the positive. The ground is grounded to the pump's mount.

Odds are, the relay's male contacts and the female connectors are corroded and need cleaning.


mbrund 11-01-2008 10:45 PM

The relays on my '92 are located just above and to the left of the Primus boilers and above the bulk oil tank on a metal plate. There are two relays, one for each pump.

Is the boiler firing and heating, just the circulation pump not working?

If so, Robert is more than likely correct, you may just have a bad relay. I believe it is the purple wire on the Primus that controls the pump (there are three molex connectors on the Primus control board, the one in the middle with the single Purple wire controls the motor relay). With the boiler operational (burning and heating water), check the voltage at the purple wire on the controler board. If you don't see 12 volts here you have some other problem (may be a bad control board), if you see 12 volts then the pump should be operating. If not, then check the relay to see if the relay is engaged by checking the voltage on the outer pin that goes to the motor. If it has voltage then the motor has an issue (or the motor ground has a bad connection), if it doesn't have voltage the relay has an issue.

aclark 11-02-2008 11:28 PM

Thanks for the info. I checked the relay and it is functioning properly but i still have no power to the pump. Also, is there only one pump on the system or is there one pump for each side/control panel? Please bear with me while I ask all of these questions.

aclark 11-02-2008 11:41 PM

Maybe I am looking at the wrong part. Can anyone verify the pump is located in line and above and in front of the boilers in the engine compartment? What I am looking at has two wires going to it and is plumbed in to the water lines for the Primus.

RGloverii 11-03-2008 12:26 AM


On my bird, one of my pumps recently stopped working. The connections on the relay were badly corroded. After replacing the relays, I inspected the actual pump, and noticed there was a ton of dirt and grime caked inside the housing from road debris.

I removed the pump, cleaned it, and lubed it. Now it works much better than before.

Perhaps your pump is so full of gunk it cannot freely spin. I suggest that as your next step. When removing the pump, be prepared to plug your water lines to avoid a loss of fluid.

mbrund 11-03-2008 01:39 AM


Originally Posted by aclark (Post 9083)
Maybe I am looking at the wrong part. Can anyone verify the pump is located in line and above and in front of the boilers in the engine compartment? What I am looking at has two wires going to it and is plumbed in to the water lines for the Primus.


Each Primus has it's own pump. The pumps are located directly behind each Primus unit. The Primus units are mounted on a plate that sets down in the side compartment, the motors are also mounted to the plate that primus boilers are mounted to, but way behind them. If you look at the back of the primus boiler, you will see a hose coming out of the top of the boiler. This is the heated water outlet from the boiler, now look directly down from that hose and you will see another hose. This is the inlet hose. Now trace that hose (it heads toward the engine) and about a foot behind the Primus boiler connected to that hose will be the motor. Sometimes the motor is quit enough you can not hear it operating over the boiler. You can put your hand on the motor housing and feel it running. The easiest way to know if the motor is operating is to remove the cap off the overflow tank (there are two, one for each Primus) and see of there is water flowing into the tank from the hose at the top of the tank. The tanks are mounted in the engine compartment to the ceiling of the engine compartment on the right side and to the left of the rear remote key panel. If water is flowing into the tanks when the boilers are operational, then the motors are working. These tanks should be kept 1/2 full of 50/50 anti-freeze/water mix.

I believe what you are are seeing (above and infront of the boilers) maybe the overheat sensors. These sensors have two wires (forget the color, they may be red), and in the middle of the sensor there is a red reset button. If the water every gets overtemp or you run low on water and steam is produced, these sensors will open up and shut down the Primus. If that happens, you have to press the red-button to reset it (they are kind of like circuit breakers, but based on temp instead of power). It's either that or the spolan valve you are refering to. The spolan valve is controlled by a switch in the overhead cabinet above the pilots chair, and is marked summer/winter. When you flip it to summer, the spolan closes and allows the hot water from the boiler to only travel through the hot water heater to heat the hot water and keeps it from traveling through the coach and heating it up.

Hopefully I have not confused you more. If you would rather talk, give me a call and I can go into additional detail on the Primus. I just rebuilt both mine two weeks ago as I had a problem with one of them, and since I had to rip it out I just did both of them.

aclark 11-03-2008 08:34 AM

Micheal, thanks alot for the information. I appreciate everyones willingness to help out. I will check the power to both pumps and see what I come up with. Thanks again. Andy.

BLUESURF 11-11-2010 11:25 AM

I too am having trouble with primus heat. On a 1991 Bird. Have two boilers in the back right side, one for right side heat and one for left.

Have a thermostat control above the driver's seat, and one back in the bedroom mounted on the back wall.

I am still trying to learn the theory behind primus heating, accurate to within one degree.

Do the boilers heat up the 50/50 antifreeze solution and just keep recirculating it?

Also when boondocking, do these boilers need to run off shore power, or will they run from 12 volt.

Phillip Wright in Rocky Mount, Virginia

Stephen 11-11-2010 11:46 AM

run off 12 volt
constant recirculation of heated coolant
the dial on the thermostat when at 12 o'clock position is approx 72 degrees the system is a split system left side of the coach and right side not front and back
your mileage may vary
We have parts

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